Gallium is a valuable metal having important uses in electronic applications. Such applications generally require ultrapure forms of gallium as even trace impurities can have radical effects upon electronic properties. A wide range of crude gallium sources exists with variety in the identity and quantity of impurities present, as for example, certain impurities which are not present in virgin (primary) gallium sources, may be present in recycled (secondary) gallium sources. Particular impurities have generally required the use of particular purification procedures. For example, both melt crystallization and electrorefining have a fair number of impurities which follow the gallium through the processing and are not removed. This limits the usefulness of such procedures for general application to all gallium sources, and necessitates special procedures for the particular problem impurities. Thus, it would be advantageous to have a purification procedure of general applicability to gallium sources to remove practically all metal impurities.
Solvent extraction hydrometallurgy has bee used to recover valuable metals, and such procedures have been disclosed for recovery of gallium. However, such procedures have not found prominent use for purification of gallium by removal of metal impurities from gallium sources.
Xiang et al in Acta Metallurgica Sinica 18 (2), 221, (1982) describe the use of a certain undefined fatty hydroxamic acid for the recovery of gallium from aqueous acid solutions.
Iwaya, Japanese Patent No. SH060 (1985) 245736, Appln. No. SH059 (1984) 101504, published Dec. 5, 1985, discloses a method of recovering gallium, using hydroxamic acid resins, described as having --C(O)NHOH groups, from high-basicity aqueous sodium aluminate solutions. U.S. Pat. No. 3,821,351 issued June 28, 1974 to M. F. Lucid discloses certain N-substituted hydroxamic acids useful as extractants for the recovery of copper, molybdenum, uranium, iron and vanadium.
A commonly assigned patent, U.S. Pat. No. 4,567,284, to Bruce F. Monzyk and Arthur A. Henn claims cobalt complexes of N-alkylalkano hydroxamic acid and involves use of such acids as cobalt extractants.
A commonly assigned application of James P. Coleman, Bruce F. Monzyk, and Charles R. Graham discloses solvent extraction procedures employing N-organohydroxamic acid extractants for recovery of gallium, and in general the procedures and agents described in that application are useful in the present invention; see Ser. No. 937,849 filed Dec. 4, 1986.
A commonly assigned copending application of Coleman and Monzyk [43-21(6836)A] filed Feb. 24, 1987, describes methods for oxidative dissolution of gallium arsenide, with preferable procedures involving use of hydroxamic acid and hydrogen peroxide, and such procedures will be useful in converting gallium arsenide source material into a form suitable for use in the present invention.
A number of other approaches to purification of gallium are known. Thus, Abrjutin et al, U.S. Pat. No. 4,362,560 discloses a vacuum-thermal decomposition process for treating various high grade gallium arsenide wastes, and also references various prior art procedures. Bird et al, Production of High Purity Gallium From Scrap Gallium, SME mini-symposium on "The Hydrometallurgy of the Rarer Metals", Dallas, 1982, pp. 59-64, describes various sources of gallium arsenide scrap and a process to produce high purity gallium therefrom; the process includes disassociation by leaching in hot aqua regia (4HCl:1 HNO.sub.3), and neutralization of the acid solution with NaOH to precipitate Ga(OH).sub.3.
Electrowinning and electrorefining are widely used procedures for recovery and purification of various metals, and the electrochemical purification of gallium has been described in an article by Lupenko and Tryb, "Removal of Microimpurities from Gallium", J. Appl. Chem., USSR 38 (3), 501 (1965). An improved process is described by John H. Wagenknecht in U.S. Pat. No. 4,026,771. The electrolytic processes are useful but have certain limitations, such as not being applicable to nonmetallic feeds or for removal of some metals close to gallium in the electromotive series and unsuitability for removal of a number of common impurities. However, the electrolytic processes are useful in conjunction with the present invention for converting the purified gallium product to metallic form, and in some instances for further purification or removal of particular residual impurities.